This invention relates to a four-cycle reciprocating-piston internal combustion engine with an unflushed ignition chamber in communication with the main combustion chamber by way of a spill port or overlow duct. This ignition chamber is associated with a spark plug and, at an angle to the latter, an injection nozzle, by means of which an amount of fuel is injected which is a fraction of the full-load quantity.
In a conventional internal combustion engine of this type (German Pat. No. 1,251,577), the volume of the ignition chamber terminating in the main combustion chamber via a spill port represents only a relatively small proportion of the total compression volume. In conjunction with the spill port of a relatively small cross section as employed in this structure, this arrangement results in a high flame exit speed and a correspondingly abrupt ignition of the taken-in amount of primary mixture. The cause of this is, inter alia, that strictly separate mixture zones are formed between the ignition chamber and the main combustion chamber. As a consequence, there results high peak pressures with a comparatively low intermediate pressure, so that the operating characteristic and efficiency, as compared to those of conventional Otto-type engines, cannot be satisfactory.
It is contemplated by this invention to construct an engine of the aforementioned type so that, with advantageous loads on the engine, i.e., a soft combustion characteristic which is desirable especially also for reasons of comfort, there results a good exhaust gas quality with especially a low proportion of nitrogen oxides.
According to preferred embodiments of this invention, an internal combustion engine of the type mentioned hereinabove is constructed so that the ratio between the volume of the ignition chamber and the total compression volume is 0.10 - 0.30 and the ratio between the volume of the spill port and the total compression volume is 0.01 - 0.25; and that the beginning of the injection into the ignition chamber, wherein approximately 2-10% of the maximum full-load quantity is injected, is in the intake stroke. In particular preferred embodiments, the beginning of the injection is at a crank angle of between 200.degree. and 300.degree. before the end of the compression stroke.
This construction of the invention leads, due to the early beginning of injection, to an extensive homogenization of the fuel proportion injected into the ignition chamber and furthermore also results, due to the relationship of the size of the ignition chamber to the injection quantity, in a satisfactory ignitability without the danger of over-enrichment in the ignition chamber. The construction also makes it possible to utilize fuels having a low octane number (regular fuels). Additionally, the arrangements of the invention provides relatively high intermediate pressures due to the given volume ratio between the ignition chamber and the total compression volume and/or between the ignition chamber and the spill port, with a relatively wide spill port and a soft engine operation. Consequently, based on the cylinder capacity of the engine, a high efficiency can also be attained for such ignition chamber engines.
For the desired, soft operating characteristic, it proves to be advantageous according to the invention to provide that, based on a reference ignition chamber with a corresponding volume and of a spherical shape, the diameter of the spill port to the diameter of the ignition chamber is at a ratio of between 0.3 and 0.7.
In one embodiment of the invention, the amount of fuel injected into the ignition chamber is either maintained at a constant value, namely independent of the load and speed, or it is controlled so that the amount injected is reduced with an increasing load and speed. U.S. Pat. No. 3,508,530 to Clawson discloses a prior arrangement with the amount of fuel injected into the ignition chamber being independent of the load and speed of the invention, while U.S. Pat. No. 3,824,965 to Clawson discloses a prior arrangement with reduction of the injected amount of fuel with inceasing load and/or speed of the engine.
According to the invention, the axes of the spark plug and the injection nozzle are oriented preferably at a mutual angle of between 60.degree. and 90.degree., whereby the danger of wetting of the spark plug is diminished, and thus the starting conditions for the engine are improved.
In another preferred embodiment, the axis of the spill port is approximately congruent with the axis of the spark plug. In other preferred embodiments, the axis of the injection nozzles lies approximately in parallel to the axis of the spill port. In yet other preferred embodiments, the axis of the injection nozzle is congruent with the axis of the spill port. A position of the axis of the injection nozzle wherein it is offset with respect to the axis of the spill is advantageous especially in case of turbulence (swirl) chambers, in certain preferred embodiments. Furthermore, a position of the axis of the injection nozzle approximately in parallel to the axis of the spill port is suitable to ensure uniform conditions in the ignition chamber and to attain a minor wall proportion. Finally, such a position of the injection nozzle can also be advantageous for obtaining a good stratification in the zone of the spill port, thus creating gradual transitions with regard to the mixture ratios. In this connection, it is to be taken into account that the amount of fuel introduced into the ignition chamber is very small and that, at least above the idling range, the main proportion of the fuel is introduced directly into the main combustion chamber, namely under the control of the throttle valve either by way of a carburetor or by way of a suction pipe injection system. In total, the design is selected so that the air-fuel ratio .lambda. over the entire partial load range of the engine is at least approximately constant and is preferably .lambda. = 1.1. In correspondence with the constant amount of fuel introduced into the ignition chamber, a relatively rich mixture is present in the ignition chamber at low load or in the idling range, while the amount of fuel fed to the main combustion chamber is dimensioned so that a lean mixture is obtained in the latter chamber during the aforementioned ranges. In the pure full-load range, the total mixture can be enriched to .lambda. &lt; 1 for reasons of attaining optimum efficiency.
Due to the early injection time for the nozzle which injects into the ignition chamber, it is possible to operate herein with a low-pressure injection nozzle, the spraying pressure of which is between about 10 and 40 bars. In this connection, the use of such injection nozzles proves advantageous which spray with a spray cone of up to about 45.degree..
Due to the fact that, as compared to engines wherein the entire amount of fuel is introduced into the main combustion chamber, a higher air-fuel ratio exists in the main combustion chamber than for the entire engine, the danger of spontaneous ignitions is reduced, and thus it is possible even with fuels having a low octane number to still attain compression ratios of up to an .epsilon. of about 14.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, plural embodiments in accordance with the present invention.